This invention is a device for operating a valve that requires a large operating torque and that requires long term reliability, such as a valve that operates at the seafloor in a deep sea.
One type of main valve that requires high torque for operation and high reliability, includes a valve that controls the flow of drilling fluid, such as a water glycol mixture, to drilling equipment that drills into the seabed. A prior main valve of this type includes two metal discs, one pivoting on the other, and with passages that come into and out of alignment. The valve passes fluid from a high pressure source to a cylinder that uses the same or different high pressure fluid as to control the flow of the drilling fluid, or blocks the high pressure fluid while connecting the cylinder to a return. A high torque for a small valve, such as 120 inch pounds is required to pivot one of the discs with respect to the other, while the discs are pressed with high force against one another to avoid leakage at 17,500 psi.
The prior valve assembly includes a pilot valve that controls the flow of fluid at 5,000 psi, and which operates the main valve. The pilot valve is operated by a current of about one ampere at 12 to 24 volts. It was not practical to use a solenoid to operate the main valve, because of the very high current necessary to produce the required actuation force, and the consequent heating.
Experience has shown that the pilot valve is the most unreliable part of the prior valve design. The pilot valve often develops hydraulic fluid leaks of the operating fluid (5,000 psi), and other problems that lead to the need to replace the valve at extreme inconvenience and cost. The main valve has proven to be very reliable but the overall reliability of the complete valve assembly has been limited by the problems with the pilot valve stage. Eliminating the problems with the pilot valve stage would produce a valve with a significantly improved reliability and a much lower operating and maintenance cost. This is especially critical in applications where access to the valve is limited, such as in subsea applications.